Hitherto, there has been known a vehicle brake control device configured to generate a braking torque by an electric motor. In the device of this type, typically, an indication current (target current) is calculated based on an operation amount of a driver-operated braking operation member of the vehicle, and the electric motor is controlled based on the indication current. Then, a braking torque that depends on the operation of the braking operation member is applied to the wheels.
In the device of this type, due to influences of the inertia (inertia moment, inertia mass) of the entire device including the inertia of the electric motor, particularly in a case of abrupt braking (upon rapid increase of braking torque) or the like, a response delay of the braking torque (a delay of rise thereof) may occur in acceleration during which the rotation speed of the electric motor is increased (e.g., when the electric motor is started) and an overshoot of the braking torque may occur in deceleration during which the rotation speed of the electric motor is decreased (e.g., when the electric motor is intended to be stopped). Therefore, particularly, at abrupt braking, it is desired to compensate for the influences of the inertia, that is, to improve responsiveness (rising performance) of the braking torque during acceleration of the electric motor and to suppress the overshoot of the braking torque during deceleration of the electric motor (improve the convergence).
As to how to cope with this problem, for example, Japanese Patent Application Laid-open No. 2002-225690 describes as follows. That is, based on a map in which indication currents and target motor rotation angles are co-related, a target motor rotation angle corresponding to the calculated indication current is determined, and a target motor rotation angular acceleration is calculated by subjecting the target motor rotation angle to the second-order differentiation. Based on the target motor rotation angular acceleration, an inertia compensation current for compensating for the influences of the inertia of the entire device is calculated. In this case, the inertia compensation current is calculated to be a positive value during acceleration of the electric motor, while the inertia compensation current is calculated to be a negative value during deceleration of the electric motor. This inertia compensation current is added to the indication current, to thereby determine a compensated indication current (target current). In this manner, the compensated indication current is calculated to be slightly larger than the indication current when the electric motor is started, thereby being capable of improving the responsiveness of the braking torque. The compensated indication current is calculated to be slightly smaller than the indication current when the electric motor is intended to be stopped, thereby being capable of suppressing the overshoot of the braking torque.
In addition, Japanese Patent Application Laid-open No. 2002-225690 also describes providing a “gradient limitation” against the indication current for performing stable control when the indication current exceeds the capacity of the electric motor.